1. Field of the Invention
The present invention relates to a method and apparatus for controlling a stepping motor, and a recording medium storing a program for carrying out the method, wherein the stepping motor is controlled while the stepping motor serves as a motor actuator for rotatably driving each of various types of air-conditioning doors used in a vehicle air-conditioning unit.
2. Description of the Related Art
As a prior art device of this type, there has been disclosed a control system in Patent Application Publication (KOKOKU) Hei 4-9685, for example.
More particularly, the control system set forth in the above Publication is provided to control the mode door in the vehicle air conditioning system. Such a control system comprises a power supply detecting means for detecting the application of the power supply voltage, a setting means for setting the initial position of the mode door, a pulse generating means for generating the driving pulse signals for the stepping motors to drive the mode door, and a mode door position detecting means for detecting a desired door position of the mode door based on a setting of the mode door switch.
In such a control system, activation of the power supply is detected by the power supply detecting means when the power supply voltage is applied, and then the detection signal is input into the setting means. Meanwhile, a set condition of the mode switch is detected by the mode door position detecting means, and then the detected result is applied to the setting means and the pulse generating means.
When the detection signal is input from the power supply detecting means to the setting means, the predetermined controls signal can be output from the setting means to the pulse generating means in order to generate the driving pulse which is needed to rotate the mode door into its initial position. Such initial position has been decided previously in response to the set position of the mode door switch.
Therefore, the predetermined driving pulse signal needed to rotate the mode door into the initial position is applied from the pulse generating means to the stepping motors. As the result of such drive, the mode door can be set at its initial position.
After this, the driving pulse signal which corresponds to the set position of the mode switch detected by the mode door position detecting means is applied to the stepping motors. As a result, the mode door can be rotated into the position according to the set of the mode switch.
In contrast, in Patent Application Publication (KOKOKU) Hei 6-81552, for example, a control system for detecting the "out-of-step" of the stepping motor has been disclosed.
More particularly, this control system is constructed to comprise a controller, a driver, a command pulse speed detecting circuit, a deviation counter, a decision circuit, and a rotary encoder as a detecting means.
The controller outputs the command pulse, which supplies commands of the rotating angle, the rotating speed, etc. to the stepping motor, to the driver which generates the pulse signal to drive the stepping motor. The driver outputs necessary pulse signals to the stepping motor based on the command pulse.
The command pulse is also input from the controller to the command pulse speed detecting circuit and the deviation counter. In the command pulse speed detecting circuit, the rotating speed of the stepping motor instructed by the command pulse is detected based on the command pulse being input.
The deviation counter receives the command pulse together with the actual information of the rotating speed of the stepping motor, which has been detected by the encoder. In the deviation counter, the deviation between the actual rotating speed and the rotating speed instructed by the command pulse is detected, and then the detected result is input into the decision circuit.
In the decision circuit, it is decided whether or not the output value of the deviation counter exceeds a predetermined value. Then, it is decided whether the output value of the deviation counter has exceeded the predetermined value, and the control signal which can compulsorily terminate the driving of the stepping motor is output from the decision circuit to the driver. Then, the predetermined value in the decision circuit is set according to the set speed of the stepping motor which is detected by the command pulse speed detecting circuit.
However, in the above-mentioned conventional apparatus disclosed in Japanese Patent Publication No. Hei 4-9685, since the initial setting of the position of the air-conditioning door is made each time the electric power supply of the vehicle air-conditioning unit is turned on, i.e., since such initial setting is forcibly made even when it is not required, the conventional apparatus is poor in efficiency. In addition, the conventional apparatus suffers from a strange noise which is often issued from the stepping motor. Namely, in the initial setting of the air-conditioning door, since the air-conditioning door is urged in a single direction, the above-mentioned strange noise is often issued from the stepping motor, which makes a user uncomfortable.
On the other hand, in the conventional technique disclosed in Japanese Patent Publication No. Hei 6-81552, it is necessary to provide an additional detection means, which increases costs of an apparatus for carrying out the conventional technique. More particularly, when the conventional technique is applied to a vehicle air-conditioning unit with a limited space, it is necessary to produce an additional space for housing the detecting means, which requires the vehicle air-conditioning unit to be modified in construction.